Gold is a highly stable metal without any catalyst activity. When the size of a gold particle is smaller than 10 nm, gold exhibits a unique room temperature activity due to meta-stable interatomic bonding of gold atoms. A nano-gold catalyst has the following three features: fast reaction rate, high selectivity, and low reaction temperature.
Applications of a nano-gold catalyst include:
(1) Oxidation of Carbon Monoxide at Room Temperature
The oxidation reaction of carbon monoxide at room temperature is a best showcase reaction for a nano-gold catalyst. At present, only a nano-gold catalyst has the capability of oxidizing carbon monoxide at room temperature. The prerequisite for an active gold catalyst is the particle size of gold needs to be less than 10 nm, with an optimum catalyst particle size of <5 nm. Another factor affecting the activity of a gold catalyst is a strong metal-support interaction (SMSI) between gold and a support. The support is preferably selected from p-type and n-type semiconductor metal oxides. Available supports include: TiO2, Fe2O3, Co3O4 and NiO, etc.
At present, although a gold catalyst can be synthesized to have a particle size less than 10 nm and posses a high activity in oxidizing carbon monoxide, it can not be commercialized due to a short lifetime and the catalytic efficiency of the catalyst. The factors affecting the lifetime of the catalyst include: an insufficient interaction between gold particles and the support. The melting point of a gold catalyst with a particle size of 5 nm is drastically reduced from the original 1337K to 700K. As a result, the gold catalyst is liable of sintering along with the progress of the reaction. And the catalyst will lose its activity when the particle size of the catalyst grows beyond 10 nm.
(2) Selective Oxidation Reaction of Hydrocarbons
The selective oxidation of hydrocarbons and aromatic hydrocarbons is an important technology for producing key intermediate materials in chemical engineering processes, e.g. preparation of an alcohol from an alkane, preparation of an epoxide from an alkene, and preparation of a hydroxyl aromatic hydrocarbon from an aromatic hydrocarbon, etc. Most of the above-mentioned processes adopt a liquid phase oxidation reaction system, which uses hydrogen peroxide as an oxidizing agent. A gas phase oxidation process cannot compete with a liquid phase oxidation process due to a poor selectivity. However, this situation is changed due to the emergence of the nano-gold catalyst. The selectivity of product for some processes can exceed 90 mol % and molecular oxygen can be used as an oxidizing agent. Even though the results are encouraging, improvements are required due to a low yield per unit catalyst. The related prior arts are listed in the following:
Selec-Con-Type of reactionCatalysttivityversionYieldRef.methanol →Au gauze1001001001)formaldehydepropylene → POAu-TiO2/SiO2932.6—2)isobutane → t-butanolAu-TiO2/SiO2851.0—2)1) C. N. Hodges and L. C. Roselaar, J. Appl. Chem. Biotechnol. 25 (1975) p609 2) T. Hayashi and M. Haruta, Shokubai, 37 (1995) p75 (3) Use of Nano-gold Catalyst in Other Chemical Reactions:
Type of reactionCatalystRef.Butadiene → buteneAu/Al2O32)Acetone → isopropanolAu films3)CO + H2 → methanolAu/ZnO, Au/ZnFe2O44)CO + H2O → H2Au/Fe2O35)NO + H2 → N2 or NH3Au/MgO6)NO + CO → N2 or N2OAu/Fe2O3, Au/NiFe2O47)NO + hydrocarbon → N2Au/ZnO, Au/Al2O38)2) T. Hayashi and M. Haruta, Shokubai, 37 (1995) p75 3) C. T. H. Stoddat and C. Kemball, J. Colloid Sci., 11 (1956) p633 4) H. Sakurai and M. Haruta, Catal. Today, 29 (1996) p361 5) D. Andreeva, T. Tabakova, V. Idakiev, P. Christov, and R. Giovanoli, Appl. Catal. A:, 169 (1998) p9 6) S. Galvagno and G. Parravano, J. Catal., 55(1978) p178 7) M. Haruta, Catal. Today, 36(1996) p153 8) A. Ueda, T. Ohshima, and M. Haruta, Appl. Catal. B:, 12 (1997) p81 
WO 00/09259 (CA 246882A1) discloses a Au/Fe2O3 catalyst suitable for CO selective oxidation in a reforming gas. Said catalyst is prepared by depositing a gold cluster with a diameter less than 4.5 nm on a granular Fe2O3 catalyst support. A method for preparing said catalyst comprises: (a) reacting a water soluble Fe(III) salt with an alkaline in an aqueous medium; (b) immersing a wet hydroxide gel thus obtained in an aqueous solution of a water soluble gold compound in order to deposit a complex gold cluster on the surface of the hydroxide gel; (c) removing water from the obtained reaction product suspension; and (d) calcining the resulting dry reaction product at 350-700° C. Although said prior art catalyst can selectively oxidize CO in a reforming gas, its CO oxidation activity at room temperature is still too low.